Conventional pulse width modulators (PWM), for example a PWM unit in a microcontroller, are generally limited in their resolution to the general system clock. Resolution in PWM peripheral units is an important parameter, determining how accurately the pulse width can be controlled. If the PWM pulse width cannot be accurately enough controlled a number of problems such as limit cycling or simply an incorrect output voltage value will occur. As stated above, typically the smallest PWM pulse width adjustment would be equal to the system clock period. On a 16 MHz device this would be 62.5 ns.
In most switched mode power supply (SMPS) applications the operational range for duty cycle turns out being only a fraction of the full range. For example, a 12V to 1.2V DC/DC buck converter would use less than 10% of the full range, reducing the effective PWM resolution by 3.3 bits. This all means that a conventional PWM used for an SMPS at 600 kHz switching frequency operating from a 16 MHz system clock would at best be able to achieve 5 bits of resolution and if it was a DC/DC converter as described above it would lose 3.3 bits of resolution, resulting in an effective control resolution of a mere 1.7 bits which is clearly undesirable.
Hence, there exists a need for an improved PWM having a high resolution.